College Chemistry Chapter 3

Stoichiometry

Law of Conservation of MassAll chemical and physical reactions must

follow the LCM.Lavoisier was the first to state this law and

he was also given credit as the founder of quantitative chemistry.

All equations must be balanced in order to adhere to the LCM.

Law of Conservation of MassRegular reactions: atoms and masses

balanceRedox reactions: atoms, masses, and

charges balanceHere there will be change in the oxidation state of

ions during the reaction. One element will be oxidized; that means that it

will lose electrons and become more positive. One element will be reduced; that means that it

will gain electrons and become more negative. A balanced equation may require that half

reactions be considered in order to balance the charges.

Redox examplesMg0

(s) + 2HCl(aq) MgCl2(aq) + H2(g)

Half reactions: Oxidation: Mg0

(s) Mg+2 + 2e-

Reduction: 2H+(aq) + 2e- H2

0

Spectator ions: Cl-(aq)

Types of ReactionsSynthesis (direct combination) – A+BC

May use elements May use compounds

Using metal oxides: get hydroxidesUsing nonmetal oxides: get acids

Decomposition (analysis) – C A+BOrdinary binary compoundsChlorates – chloride salt and oxygenCarbonates – oxides and carbon dioxideHydroxides – metal oxide and waterAcids – nonmetallic oxide and water

ExamplesOrdinary binary compounds

2NaCl(s) 2Na0(s) + Cl20

(g)

Chlorates – chloride salt and oxygen2KClO3(s) 2KCl(s) + 3O2(g)

Carbonates – oxides and carbon dioxideBaCO3(s) BaO(s) + CO2(g)

Hydroxides – metal oxide and waterNaOH(l) Na2O(s) + H2O(l)

Acids – nonmetallic oxide and waterH2SO4(s) SO3(g) + H2O(l)

Types of ReactionsSingle displacement – A + BC AC + B

Must use activity series to determine if reaction happens

May be used with halogens with F2 > Cl2 > Br2 > I2

Double replacement – AB + CD AD + CBMust consider the driving forces to determine if

reaction happensFormation of a precipitateFormation of a gasFormation of waterFormation of a small molecular compound

Solubility RulesFormation of a precipitate occurs if the product

is insoluble in aqueous solution. Soluble compounds are those containing

NH4+, Li+1, Na+1, K+1, Rb+1, Cs+1

NO3-

C2H3O2- except with Ag+

Cl-, Br-, I- except with Ag+, Hg2+2, and Pb+2

SO4-2 except with Sr+2, Ba+2, Hg2

+2, Pb+2

Solubility Rules

Insoluble compounds are those containingS-2 except with NH4

+, Li+1, Na+1, K+1, Rb+1, Cs+1, Sr+2, Ba+2, Ca+2

CO3-2 except with NH4

+, Li+1, Na+1, K+1, Rb+1, Cs+1

PO4-3 except with NH4

+, Li+1, Na+1, K+1, Rb+1, Cs+1

OH- except with NH4+, Li+1, Na+1, K+1, Rb+1, Cs+1, Sr+2,

Ba+2, Ca+2

REMEMBERDiatomics such as H2, O2, N2, F2, Cl2, Br2, or

I2The charge on a compound must net zero.The charges on the representative

elements are predictable; those on the transition elements are not except for zinc, silver, and cadmium.

Types of ReactionsCombustion – one reactant will be oxygen

and the other one may be an organic compound, a metallic compound, or a nonmetallic compoundComplete – occurs when there is excess

oxygen CO2(g) + H2O(l)

Incomplete – occurs when there is a limited amount of oxygen CO(g) + H2O(l)

Types of Solution ReactionsPrecipitation reactions – a precipitate forms as

a result of two solutions reacting in solutionAcid-base reactions (neutralizations) – water

and a salt form as a result of an acid and a base reacting in solution (may be a titration)

Oxidation-reduction reactions (redox) – products form such that the charges on reactant ions change as the reaction proceeds. Two half reactions are sometimes required to

determine the balanced equation. May be in acidic or basic solution.

Atomic and Molecular WeightsAtomic masses are based on the standard

of carbon-12. The masses on the periodic table are not

the mass of any isotopes; they are the weighted average of all the isotopes.

Empirical FormulasDirectly

MassesPercent composition

Combustion analysis